Class H amplifiers are known to improve the efficiency of conventional Class AB amplifiers. Traditional Class G and Class H amplifiers require multiple power supplies for providing positive and negative supply voltages. Recently, combining a voltage generation method to generate a set of positive and negative supply voltages with selectable modes (to generate different bipolar supply voltages) was found to be an efficient and cost effective way to implement Class G or Class H amplifiers.
A power generation method with a dual mode charge pump is first proposed by U.S. Pat. Application Publication No. 2008/0044041, which uses two flying capacitors and eight controlled switches. Later, U.S. Pat. No. 7,626,445 proposes an improved dual mode charge pump which uses only one flying capacitor and six switches to generate bipolar supply voltages, thereby reducing the die area and costs. However, the generated bipolar supply voltages are all related to the input voltage VDD of the dual mode charge pump, as being equal to either ±VDD or ±cVDD, where c is a fractional ratio number. For example, in U.S. Pat. Application Publication No. 2008/0044041, referring to FIG. 1, when the positive supply voltage Out+ is 1.6V, the negative supply voltage Out− must be −1.6V, and the input voltage Vbatt can only be 1.6V or a fractional times, for example ⅔, of 1.6V, and additional capacitors are needed to implement the fractional times of 1.6V. The input voltage Vbatt is fully limited by the output supply voltages Out+/Out−, thus reducing flexibility of system applications.
Moreover, in the known dual mode charge pump as disclosed by U.S. Pat. Application Publication No. 2008/0044041 and shown in FIG. 1, the common mode voltage Vcm is loosely controlled by the switching actions, resulting in larger common voltage drift, especially when the load currents drawn from the supply voltage output terminals Out+ and Out− are not balanced.